jQuery is the most widely-used JavaScript library, and is used in more than half of all major websites.
jQuery makes web development easier to use by providing a number of 'helper' functions. These help developers to quickly write DOM (Document Object Model) interactions without needing to manually write as much JavaScript themselves.
jQuery adds a global variable with all of the libraries methods attached. The naming convention is to have this global variable as <code>$</code>. by typing in <code>$.</code> you have all the jQuery methods at your disposal.